The Dell OS10 Router must be configured to have Gratuitous ARP disabled on all external interfaces.

A gratuitous ARP is an ARP broadcast in which the source and destination MAC addresses are the same. It is used to inform the network about a host IP address. A spoofed gratuitous ARP message can cause network mapping information to be stored incorrectly, causing network malfunction.

Review the Dell OS10 Switch configuration to determine if gratuitous ARP is disabled on all external interfaces.

Verify that gratuitous ARP has not been enabled on each external interface by checking that the following has not been configured:

ip arp gratuitous update

If gratuitous ARP is enabled on any external interface, this is a finding.

Configure the Dell OS10 Switch to disable gratuitous arp on all external interfaces as shown in the example below:

OS10(config)# interface ethernet 1/1/1 OS10(conf-if-eth1/1/1)# no ip arp gratuitous update